Unhappy [Q] Problems updating Huawei Ascend P1 (U9200)

Hi

My mothers Huawei Ascend P1 (U9200) is somewhat unstable with the original ROM. Currently its running Android 4.0.4 with B103 firmware. When I try to update the firmware to the latest version from Huawei, I get a error like this: assert failed apply_patch_check("/system/app/MusicFX.apk (Status code 7)

From what I read, this file is either changed or missing and the hash doesn't match the version needed for update. In my case, the file is missing from the /system/app folder. I tried copying a version from the web into the folder, but I don't have permission as root is needed.

When I try to root the phone, using the guides from XDA, I get stuck at the bootloader. Whenever I try to boot into bootloader, the phone gets stuck with the Huawei logo. I can't get in contact with it with "fastboot devices" or "adb devices".

Now I'm out of ideas. What can I do to update the phone?

Before I tried the things above, I wiped cache and system data (factory reset).